1. Field of the Invention
The present invention relates generally to a channel mode converting method of a wireless portable Internet system, and in particular, to a channel mode converting method for converting a diversity channel mode into a band Adaptive Modulation and Coding (Band AMC) channel mode.
2. Description of the Related Art
The wireless portable Internet is a next-generation communication system that supports mobility in local area data communication using a fixed Access Point (AP) such as a conventional wireless Local Access Network (LAN). Various standards have been provided for such a wireless portable Internet, including international standards based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16d/e standard groups.
FIG. 1 is a ladder diagram for converting a conventional diversity channel mode into a Band AMC channel mode and for partially changing a band of an AMC channel mode.
As shown in FIG. 1, when a terminal requests to convert a channel mode and a channel state, that satisfies a conversion condition for converting a diversity channel mode into an AMC channel mode, the terminal transmits a band changing request message to the AP through a Channel Quality Indicator CHannel (CQICH) for reporting quality information of the channel to the AP in step S10. When the AP receives the band changing request message, the AP transmits a channel quality information request message (REP_REQ) to the terminal thereby satisfying the channel mode conversion conditions to request an average Carrier to Interference Noise Ratio (CINR) information of the respective bands in step S20.
The terminal forms a channel quality information response message (REP_RSP) including the CINR information of five optimum bandwidths satisfying the conversion conditions for converting the diversity channel mode into the AMC channel mode in step S25, and transmits a Bandwidth Request code (BR code) to the AP for requesting necessary resources for transmitting the REP_RSP in step S30. The AP receives the bandwidth request code, allocates an uplink resource that is capable of transmitting a resource allocation request header to the terminal in step S40, and in step S50, the terminal receives the allocated uplink resource and transmits the bandwidth information for transmitting the REP_RSP to the AP using the bandwidth request header.
In step S60, the AP allocates the requested bandwidth to the terminal using an uplink map, and in step S70 the terminal transmits the Band AMC to the CQICH through the allocated bandwidth. In addition, in step S80 the terminal transmits the REP_RSP using a frame having transmitted the Band AMC, and then, in step S90, transmits data to the AP through the AMC channel mode.
In this manner, the diversity channel is converted into the AMC channel mode, and the processes shown in FIG. 1 are repeated so as to change at least part of the five optimum bands selected while the terminal uses the AMC channel mode.
In one of a process for converting the diversity channel mode into the AMC channel mode and a process for changing a part of the bandwidths used in the AMC channel mode, it is difficult to recognize the CINR of the respective bands included in the REP_RSP as the CINR of the present band because a large delay occurs before the terminal receives the REP_REQ and transmits the REP_RSP to the AP.
Additionally, in order to correct the difference, the CINR reported to the REP_RSP using the CQICH is increased or decreased per dB. However, when the present CINR is significantly different from the REP_RSP CINR, the time delay is still generated until the difference is corrected, and accordingly, transmission errors are increased at the downlink data transmitted during the delay time.
Further, the REP_RSP is transmitted to the same frame as the CQI of the changed channel mode or is transmitted after the CQI of the changed channel mode has been transmitted. However, the CQI and the REP_RSP is respectively transmitted from a physical layer and a Media Access Control (MAC) layer through the respective resources that are independently allocated. Accordingly, it is difficult to perform transmission synchronization between the changed channel mode CQI and the REP_RSP.